Is there a way to make PHP's SplHeap recalculate? (aka: add up-heap to SplHeap?)
I was solving very similar problem recently, it seems like SPL doesn't support updates. So
I had to write my own heap.
It isn't extra efficient, but it does what I need and it's much faster than sorting an array repeatedly... SPL heap is still much faster though...
here it is...
class heap{ public $members=array(); // these two are just for statistics private $swaps=0; private $recurs=array('lups'=>0, 'ldowns'=>0); public function insert($val){ if(is_array($val) && empty($this->members)){ // because heapify is (in theory) more efficient foreach($val as $v){ $this->members[]=$v; } $this->heapify(); }else{ $emptyPosition=count($this->members); // count(members) gets index of first empty position, not last key $this->members[]=$val; // puts $val in $this->ladderup($emptyPosition); } } public function heapify(){ /* in case all the heap is broken, we can always use this to repair it. It should be more efficient to fill $members randomly and "repair" it with heapify after, than inserting things one by one*/ $start=max(0, floor( (count($this->members)-1)/2)); // find last parent for($i=$start;$i>=0;$i--){ $this->ladderdown($i); } } private function ladderdown($index){ // recursively sifts down $index $this->recurs['ldowns']++; /* indexes of children they are stored at parent_position*2 and parent_position*2+1 but becouse php uses null-based array indexing, we have to modify it a little */ $iA=$index*2+1; $iB=$index*2+2; if($iA<count($this->members)){ // check if children exist if($iB<count($this->members)){ if($this->compare($iA, $iB)>=0) $bigger=$iA; // if both exist, compare them, cause we want to swap with the bigger one ; I'm using ">=" here, that means if they're equal, left child is used else $bigger=$iB; }else{ $bigger=$iA; // if only one children exists, use it } if($this->compare($bigger, $index)>0){ // not using ">=" here, there's no reason to swap them if they're same $this->swap($bigger, $index); $this->ladderdown($bigger); // continue with $bigger because that's the position, where the bigger member was before we swap()ped it } } } private function ladderup($index){ // sift-up, $this->recurs['lups']++; $parent=max(0, floor( ($index-1)/2)); // find parent index; this way it actualy swaps one too many times: at the end of sift-up-ing swaps the root with itself if($this->compare($index, $parent)>0){ $this->swap($index, $parent); $this->ladderup($parent); } } public function root(){ if(count($this->members)){ return $this->members[0]; } return false; } public function extract(){ // removes and returns root member if(!count($this->members)) return false; $this->swap(0,count($this->members)-1); // swaps root with last member $result=array_pop($this->members); // removes last member (now root) $this->ladderdown(0); // root is on wrong position, sifts it down return $result; } public function update($index, $value){ if($index<count($this->members)){ $this->members[$index]=$value; $this->ladderup($index); $this->ladderdown($index); } } public function delete($index){ // removes index from heap the same way as root is extracted $this->swap(count($this->members)-1, $index); // swaps index with last one array_pop($this->members); $this->ladderup($index); $this->ladderdown($index); } private function swap($iA, $iB){ // swaps two members $this->swaps++; $swap=$this->members[$iA]; $this->members[$iA]=$this->members[$iB]; $this->members[$iB]=$swap; } private function compare($iA, $iB){ $result=$this->members[$iA] - $this->members[$iB]; return $result; } public function stats($text=""){ // prints and resets statistics echo "STATS: $text... Sift-ups: ".$this->recurs['lups']." Sift-downs: ".$this->recurs['ldowns']." Swaps: ".$this->swaps." <br>"; $this->recurs=array('lups'=>0, 'ldowns'=>0); $this->swaps=0; }}//here's how to use it...$h=new heap;for($i=0; $i<10000; $i++){ $h->insert(rand(1,1000));}$h->stats("after inserting one-by-one");while($biggest=$h->extract()); // note that $h->extract might return FALSE, but might return zero as well, if there was zero in the heap$h->stats("after extracting all roots (like in heapsort)");echo "Now, heap is empty. Let's try whole array at once <br>";for($i=0; $i<10000; $i++){ $a[]=rand(1,1000);}$h->insert($a); // inserting whole array here, so heap will use more efficient heapify()$h->stats("after heapify");echo "let's update two indexes<br>";$h->update(1234,44444);// sure on top$h->stats("after update");$h->update(8888,40000);// second place$h->stats("after update");echo "extract biggest three indexes<br>";echo $h->extract()." - this should be 44444<br>";echo $h->extract()." - this should be 40000<br>";echo $h->extract()." - this should be biggest number given by rand(1,1000)<br>";$h->stats("after three extracts");while($h->extract());$h->stats("after extracting the rest");and result is:
STATS: after inserting one-by-one... Sift-ups: 22651 Sift-downs: 0 Swaps: 12651
STATS: after extracting all roots (like in heapsort)... Sift-ups: 0 Sift-downs: 116737 Swaps: 116737
Now, heap is empty. Let's try whole array at once
STATS: after heapify... Sift-ups: 0 Sift-downs: 12396 Swaps: 7396
let's update two indexes
STATS: after update... Sift-ups: 11 Sift-downs: 1 Swaps: 10
STATS: after update... Sift-ups: 13 Sift-downs: 1 Swaps: 12
extract biggest three indexes
44444 - this should be 44444
40000 - this should be 40000
1000 - this should be biggest number given by rand(1,1000)
STATS: after three extracts... Sift-ups: 0 Sift-downs: 42 Swaps: 42
STATS: after extracting the rest... Sift-ups: 0 Sift-downs: 116652 Swaps: 116652
You will have to modify it a bit, but anyway, hope it helps..